This invention relates to optical surfaces commonly referred to as Fresnel surfaces. Fresnel surfaces are commonly used to direct and/or focus light in desirable ways and have remained largely unchanged since their invention nearly 200 years ago. Such surfaces commonly consist of a multitude of equidistant grated protrusions formed on a flat rigid material. They are commonly structured in concentric circles in a first embodiment or in parallel rows in a second embodiment such that both embodiments direct light in desirable ways. Fresnel gratings can perform transmissive diffraction, reflective diffraction, refraction, and/or reflection. The general advantages of Fresnel optics include the performance simulation of optical lenses, prisms, and mirrors with significant reductions in material, thickness and consequently dramatically lighter weight and less bulky optics.
Heretofore, the designs of flattened Fresnel type lens, prism, and mirror structures have always been rigid and have not been variable regarding angular pitch and surface curvature. Commonly these devices were cut or molded into transparent plastic or glass in the case of transmissive members or coated with reflective materials in the case of reflective members. The angles and curves once cut thereon not being variable. Adding angular and curvature adjustability to Fresnel structures as described herein is a significant advancement now possible due to the present novel structures which utilize the many advances in the transparency and elasticity of polymer technology. Transparent or reflective, highly elastic extrusions welded and assembled to form a Fresnel optical membrane as described herein are angularly tunable by actuating a first rigid member relative to a second rigid member. Curves formed by the Fresnel optical membrane are tunable by varying fluid pressure in communication with the optical membrane. Tunable angles and curves formed by the optical membrane as described herein causes light to be refracted, reflected and/or diffracted predictably and reliably. In the transmissive embodiments, curves formed by the Fresnel optical membrane surfaces and a fluid with an index of refraction in communication therewith, cause light to be redirected as desired through the processes of refraction and/or diffraction. In the reflective embodiments, identical Fresnel membrane structures in conjunction with reflective properties or in communication with a reflective material and operated identically forms reflective surfaces whereby electromagnetic energy is redirected by the process of reflection and/or reflective diffraction.
Prior art teaches the use of flexible membranes such as is depicted in FIG. 1 from U.S. Pat. No. 5,684,637 (Floyd, 1997). The membranes are actuated to form a convex lens of desired focal length by varying a fluid with a refractive index contained there between. This structure and those abundantly found in prior art that are similarly actuated when used in small applications can reliably provide a range of focal lengths and coherent focal points. In many applications however, especially where the volume, physical size and weight of fluid are a consideration, an alternate approach utilizing Fresnel structures to provide coherent variable focal lengths is needed. The present invention achieves these objects with significantly reduced thickness, weight and volume.
Prior art teaches the use of a flexible mirror membrane actuated by fluid pressure such as is depicted in FIG. 2 from U.S. Pat. No. 4,890,903 (Treisman et al, 1990). Such a fluid mirror membrane can be used in some small applications where thickness is not a factor. In larger applications or where absolute mirror thickness is a consideration, the variable membrane mirror composed of Fresnel surfaces as disclosed herein is a useful unanticipated advancement over the prior art.
Prior art teaches the use of actuating rigid structures to reliably alter the path of electromagnetic energy. FIG. 3 from U.S. Pat. No. 5,166,831 (Hart, 1992) discloses the actuation of rigid planar members to vary a liquid prism angle. This and similar prior art is useful for some small applications. In large applications, the volume, physical size and weight of fluid required in these structures makes them prohibitive engineering problems. To eliminate the engineering problems of prior art, an alternate approach utilizing variable Fresnel structures to variably alter the course of electromagnetic radiation is required. Additionally, the Hart structure can not achieve a variable focal length (nor did Hart intend it to). Whereas the present invention can reliably achieve a coherent variable focal length.
Prior art discloses the use of variable lenslets. FIG. 4 from U.S. Pat. No. 5,774,273 (Bornhorst, 1998) depicts a hexagonal grid and a transmissive membrane. This system uses fluid pressure to push the membrane through the grid and thereby produces an array of variable lenslets. This lenslet array can not achieve a truly coherent focal point. Nor can this structure reliably deliver a single variable focal point. Additionally, due to the grid structure, much of the electromagnetic radiation is lost into the grid. The hexagonal structure is used to minimize the light loss due to absorption by the grid structure (if the grid had round holes, the grid would absorb even more energy). But the hexagonal structure introduces the problem of lenslet distortion because the curvature of the membrane will be distorted into a rippled curve (caused by non uniform stretching when conforming to the hexagonal shape) when being stretched through anything other than a round structure. The round hole and smooth curve are required for imaging optics when used in conjunction with and elastic membrane. The Bornhorst grid structure forces a compromise between the loss of optical integrity when using a hexagonal grid and loss of optical efficiency when using a round grid. The present invention can achieve the objects of a variable coherent focal point and length with nearly one hundred percent efficiency and with nearly no distortion. For all of these reasons, the new art embodied in the variable Fresnel structure disclosed in the present application is a significant unanticipated advancement over prior art.
Prior art FIG. 5 from U.S. Pat. No. 5,774,273 (Bornhorst, 1998) incorporates several independently variable arrays of fluid pressure variable lenslets into one collective structure. Again, the structure disclosed can not deliver a truly coherent focal point. Nor can it produce a variable focal length. This structure and the actuation methodology is not adequate for the purposes of a coherent variable lens with variable focal point and focal length. Each of these independent lenslet arrays can be directed into a similar direction but their grid shapes and positioning prohibit usage in any imaging optics applications. The new art disclosed in the present application avoids the problems associated with the lenslet formed by fluid pressure forcing a membrane through a grid structure. Further all of the new structures of the present invention can be used together to produce a coherent optic with variable focal length and a true focal point. These are all significant advancements unanticipated, unaddressed, and unachievable by prior art.
The variable prismatic surface of prior art FIG. 6 from U.S. Pat. No. 5,774,273 (Bornhorst, 1998) can incoherently simulate a focal point. This may be adequate for some imprecise lighting applications but is not adequate for any coherent applications. Specifically since the riser of the structure is not parallel to the light source, (but instead forms a second surface in the path of the light) a high percentage of light is either absorbed, reflected, or refracted by the secondary angle formed by the riser. This causes light rays to travel in undesired directions and further increases waste within the system. Waste of energy may be tolerable where excess energy can be pumped into the system such as in some lighting applications where efficiency is not a factor. But such waste is not tolerable in a coherent optical system especially where input energy is finite. Moreover the art taught in Bornhorst teaches that lenslet surfaces may be either variable with respect to curvature or be variable with respect to angle. None of the prior art membranes are variable with respect to both angular pitch and curvature. The new art disclosed in the present application efficiently and coherently redirects electromagnetic energy. Surfaces of the present application are true variable Fresnel structures that can be reliably varied with respect to angular pitch and curvature simultaneously and efficiently.
FIG. 33 prior art depicting diffraction gratings illustrates rigid diffraction gratings long known in the art. FIG. 33 is taken from Pedrotti, S. J., Introduction to Optics, Prentice-Hall Inc., N.J., 1993, Page 357. It depicts rigid Fresnel gratings. Specifically (b) is a blazed transmissive grating and (d) is a blazed reflective grating. Rigid gratings such as these are widely used in optical applications today. The prior art reference includes a discussion about how the angular pitches that are blazed onto the grating surfaces effect the efficiency of the structure in performing diffraction in different applications. No mention is made in prior art to any Fresnel structures incorporating variability regarding angular pitch and curvature in a single structure. The present invention achieves variable Fresnel transmissive and reflective surfaces which can be predictably and reliably changed with regard to angular pitch and curvature.
FIG. 34 prior art depicts adaptive optics methodologies. FIG. 34 is taken from Alloin, D. M., Adaptive Optics for Astonomy, Kluwer Academic Publishers, Netherlands, 1993, Page 152. It describes the variable reflective structures previously known in the art. While the diagrams depict wide dynamic ranges of motion, in practice the dynamic ranges are very minute. They are sued to control for distortions in astronomical observations. While the prior art does include actuating membranes with precision, it does not include any references to actuating Fresnel structures reliably with regard to angular pitch and curvature. The present Fresnel membrane invention can reliably and predictably be altered simultaneously with regard to angular pitch and curvature. IT also provides a dramatically great dynamic range of variability compared to prior art. The present invention also provides a truly coherent focal point. The combination of all of these advantages represents a significant advancement over prior art. The present invention also achieves membrane actuation with dramatically fewer actuators than utilized in prior art, this is much more conducive to light weight optics. which is one of the historic cornerstones of Fresnel structures.
FIG. 35 prior art depicting actuation means for adaptive optics. FIG. 35 is taken from Alloin, D. M., Adaptive Optics for Astonomy, Kluwer Academic Publishers, Netherlands, 1993, Page 155. Many actuation means are known to the prior art. Such means can all be utilized with the present invention. In some embodiments, the present invention actually uses two actuation means simultaneously. The first means being actuation of a rigid structure which causes the Fresnel membrane to be actuated with regard to angular pitch. The second means being fluid pressure in communication with the Fresnel membrane which causes the membrane to be actuated with regard to curvature. No prior art references utilize the dual actuation strategy to achieve simultaneous angular and curvature variability.
After a review of prior art it becomes clear that variable Fresnel structures as disclosed herein are an unanticipated significant advancement over the prior art. Neither the present novel concentric circular embodiment disclosed herein nor the present novel parallel grated surface embodiment disclosed herein have been achieved or anticipated in prior art. The former is capable of achieving a coherent focal point and the later performs transmissive and reflective diffraction with much greater efficiency than the prior art. Thus, the new art disclosed herein solves problems in novel unanticipated and unaddressed ways compared to the prior art. Disclosed herein is the use of concentric elastic stretchable and collapsible surfaces which enable one optical device to incorporate alterable Fresnel surfaces or surface angles and surface curves. Also disclosed herein are is the use of variable parallel Fresnel surfaces or surface angle and surface curves. Such Fresnel surfaces in each configuration are made to be permanently variable such that one optical device has alterable focal lengths or can otherwise continually be reconfigured in real time to redirect electromagnetic radiation as desired.
Our society increasing relies on accurately and reliably directing electromagnetic radiation for communications, science, photography, illumination, entertainment, telescopy, medicine, and magnification, etc. Flexible Fresnel concentric circular structures and parallel structures as described herein add important advantages for these and other important objects. Moreover, abundant and valuable benefits provided by such structures have been heretofore unrecognized and not addressed in prior art.
In the first transmissive embodiment, the invention described herein incorporates a first fluid with a first refractive index in a first series of concentric surfaces and a second fluid with a second refractive index in a coplanar second series of concentric surfaces. The two surfaces being adjacent to one another alternating between a concentric circle of the first then a concentric circle of the second then the first and etc. Wherein each circular surface in the series of first and second fluid surfaces are separated by a transparent barrier with elasticity. Additionally, fluid can be added or subtracted to each concentric circle as desired through ports in their otherwise sealed chambers. The structure and process described produces a refractive and/or diffractive optical component which is variable as to its focal length and transmittance direction.
In the second transmissive embodiment, the invention described herein incorporates a first fluid with a first refractive index in a first series of parallel surfaces and a second fluid with a second refractive index in a coplanar second series of parallel surfaces. The two surfaces being adjacent to one another alternating between a surface of the first then a surface of the second then the first and etc. Wherein each surface in the series of first and second fluid surfaces are separated by a transparent barrier with elasticity. Additionally, fluid can be added or subtracted to each surface as desired through ports in their otherwise sealed chambers. The structure and process described produces a refractive and/or diffractive optical component which is variable as to its angular pitch and curvature.
In the first reflective embodiment, the invention described herein incorporates a series of concentric reflective surfaces. Wherein each concentric surface is described by an elastic member which is variable as to angular pitch and curvature. The structure and process described produces a reflective and/or diffractive optical component which is variable as to its focal length and reflective direction.
In the second reflective embodiment, the invention described herein incorporates a series of parallel reflective surfaces. Wherein each parallel surface is described by an elastic member which is variable as to angular pitch and curvature. The structure and process described produces a refractive and/or diffractive optical component which is variable as to its focal length and reflective direction.
Accordingly, several objects and advantages of my invention are apparent. Optical elements manufactured to incorporate the structures described have alterable focal lengths. Once deployed in the field they can be tuned to direct electromagnetic energy as desired. They then can be retuned nearly instantly to many different specifications repeatedly and predictably. The applications for lenses and mirrors with a variable focus length are far too numerous to individually enumerate herein. Clearly objects such as illumination, entertainment, communications, science, photography, telescopy, medicine, materials science and magnification (among many others) will all benefit from this new technology.
Further objects and advantages will become apparent from a consideration of the drawings and ensuing description.